1. The Field of the Invention
The invention relates to a telecommunication system comprising a plurality of communicatively coupled radio transmitter stations, wherein the radio transmitter stations are configured for exchanging information via a backhaul link to reduce intercell interference
2. The Relevant Technology
Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. The use of the term “background” is inclusive of the term “context.” Thus, the following section provides both context for the disclosure and may also provide patentable support for the claims.
Mobile communication systems, also known as cellular telecommunication systems, typically comprise a plurality of adjoining communication cells, wherein each cell is determined by the radio range of the stationary transceiver station. Stationary transceiver stations are known as base stations in the early mobile telecommunication systems such as GSM or GPRS or as eNodeB in the UMTS or as access points in wireless LAN systems. In the following the stationary transceiver stations are called base stations. Each cell, i.e. the base station within a cell, may serve a plurality of mobile stations by providing a radio link for up- and downlink communication, wherein a mobile station can be a cell phone or a so-called smartphone or any other device capable of exchanging information via the radio link with the base station. Though the devices actually may be mobile or non-mobile, i.e. geographically fixed, the following description deploys the term mobile device. Note that the invention shall not be limited to any particular hardware or radio communication protocol.
When a base station transmits information to a mobile station, i.e. downlink communication, the base station typically does not radiate the signal with its maximum power. Instead the radiation parameters including radiation power are adapted according to the channel properties. However, at the receiving mobile station the signal from the base station is received with interference, i.e. the received signal is a superposition of a plurality of signals, i.e. the received signal comprises the desired signal as well as interfering signals of a plurality of sources.
In particular mobile stations located at the borderline of a cell will suffer from signals radiated by the at least one adjacent cell, since the radio range of each cell overlaps adjacent cells depending on the transmission power of the base stations. Accordingly the mobile station located at an edge of a cell will suffer from so-called inter cell interference upon reception, since radio signals radiated by base stations of adjoining cells interfere, i.e. superpose, with signals radiated by the base station currently associated with the mobile station.
To mitigate these adverse effects of inter cell interference it has been proposed to optimize the radiations by beamforming based on information exchange between base stations of adjoining cells. By directing the radiation beam of a base station to an associated and intended mobile station, the interference to other mobile stations caused by that radiation can be reduced. In this way the overall performance of the system may be improved by reducing inter cell interference. However, the optimization may require several iterations of beamformer adaptation and information exchange. Since conventional systems suffer from communication delays caused by transmission delays in the connecting backhaul link, the entire optimization process is slowed down. Further, existing optimization schemes cannot tolerate concurrent beamformer adaptations; that is, the base stations have to accomplish their adaptations in a sequential fashion. Consequently, conventional systems require a synchronization mechanism for their optimization process. Hence it is an object of the invention to at least mitigate these problems, i.e. to speed-up this optimization process and to enable an optimization process in networks without any synchronization mechanisms.